As the performance requirements of both civil and military aircraft increases, conventional control technologies using mechanical linkages cannot relieve the pilot from higher mental and manual control activity. As such, today's high performance aircraft as well as some transport aircraft use “fly-by-wire” sidesticks and center sticks also referred to as “control columns”.
These fly-by-wire control columns simulate tactile feedback relating to the control surfaces of the aircraft to the control columns.
In a “passive” control column, the pilot feels spring or damper forces according to the applied deflection of a stick of the control column relative to mechanical ground. The deflection of the stick is the control input from the pilot to a flight control computer (FCC) relating to the desired pitch and/or roll The tactile forces are realized by a spring and damper package operably acting on the stick. In such a passive control column, the pilot's controller forces (i.e. tactile feel) are usually fixed.
A drawback of this passive control concept, as opposed to conventional controllers, is that the pilot loses the contact with the control surfaces of the aircraft and loses contact with the second pilot in the cockpit. As such, the pilot loses tactile information and can only use visual cues to inform him about the actual flight state and available trim control power as well as what the other pilot is doing. Further drawbacks relate to the fact that the feedback profile cannot be adjusted to compensate for other changes in the flight state of the aircraft or control surfaces such as due to changes in, for example, altitude, weather, or mechanical failures of the control surfaces.
In a “direct drive active” control column, the pilot experiences a simulated control force through the use of elaborate servo systems alone. In the direct drive active control system, a motor, drive electronics, and a high bandwidth closed loop force and damping control algorithm are used to provide the tactile feedback directly to the stick simulating the tactile feedback of the control surfaces of aircraft. By using this high bandwidth system, the system is expensive and bulky due to the increased number of sensors, and the complexity of the control system. Further, it is contemplated that in these direct drive active systems, that if the motor fails or locks-up, the stick can become locked thereby preventing the pilot from controlling the aircraft. Alternatively, if the control electronics fail, no resistance may act against manipulation of the stick such that the pilots cannot properly or easily manipulate the deflection of the sticks to provide the desired inputs to the FCC. To correct for this, unnecessary redundancy must be built into the system to avoid the mechanical and/or electrical failures.
It is desired to provide an adjustable tactile feedback system for a control column that incorporates the benefits of an active system but that can be transitioned to a passive system in the event of failure in the active portion of the control column.